chore: upgrade to ESLint 9, migrate configuration file to flat format

.gitattributes

@@ -14,6 +14,7 @@
 *.less       text eol=lf
 *.md         text eol=lf
 *.MF         text eol=lf
+*.mjs        text eol=lf
 *.Module     text eol=lf
 *.pl         text eol=lf
 *.pom        text eol=lf

eslint.config.mjs

@@ -0,0 +1,46 @@
+import js from '@eslint/js';
+import sonarjs from 'eslint-plugin-sonarjs';
+import * as unicorn from 'eslint-plugin-unicorn';
+import prettier from 'eslint-plugin-prettier/recommended';
+import globals from 'globals';
+
+export default [
+    {
+        ignores: ['**/*.min.js', '**/build/**'],
+    },
+    js.configs.recommended,
+    sonarjs.configs.recommended,
+    unicorn.configs['flat/recommended'],
+    prettier,
+    {
+        languageOptions: {
+            globals: {
+                ...globals.browser,
+                ...globals.es2021,
+                jQuery: false,
+                $: false,
+                _: false,
+                up: false,
+                fluid: false,
+            },
+        },
+        rules: {
+            'no-redeclare': [
+                'error',
+                {
+                    builtinGlobals: false,
+                },
+            ],
+            'sonarjs/cognitive-complexity': 'off',
+            'sonarjs/no-duplicate-string': 'off',
+            'unicorn/filename-case': 'off',
+            'unicorn/no-array-callback-reference': 'off',
+            'unicorn/no-for-loop': 'off',
+            'unicorn/no-null': 'off',
+            'unicorn/no-this-assignment': 'off',
+            'unicorn/numeric-separators-style': 'off',
+            'unicorn/prefer-module': 'off',
+            'unicorn/prefer-spread': 'off',
+        },
+    },
+];

gradle.properties

@@ -89,7 +89,7 @@ logbackVersion=1.3.5
 lombokVersion=1.18.32
 mockitoVersion=4.11.0
 luceneVersion=8.11.2
-nodejsVersion=20.9.0
+nodejsVersion=20.13.0
 oauthVersion=20100527
 orgJsonVersion=20240303
 personDirectoryVersion=1.8.11